The present invention particularly relates to controlled operation of dampers in heating and air conditioning systems, especially high volume air conditioning (HVAC) systems, and will be described with particular reference thereto. The invention relates more generally to controlled operation of air cylinders and pneumatic/mechanical transducer systems, particularly for controlling fluid flow.
In heating and air conditioning systems, conditioned air is distributed through a house, office building, or other structure through air ducts. Typically, the conditioned air is forced through a duct at a constant air speed, and control of the heating or cooling for a particular room or area of the house, office building, or other structure is effected by partially restricting air flow through a duct using one or more strategically placed dampers.
The damper setting is typically effected through a pneumatic actuating system that includes an electropneumatic transducer, such as an air cylinder controlled by an electronic air pressure regulator, which operates on the damper. The air pressure regulator pressurizes or exhausts the air cylinder to cause an actuating arm of the air cylinder to move, thus causing the damper setting to be adjusted.
A problem arises in that air cylinders and other pneumatic devices can exhibit hysteresis, pressure drift, frictional settling delays, and other operating non-linearities and non-regularities. These non-regularities are usually air cylinder-specific, and may be different even for nominally similar air cylinders of the same make and model. Moreover, the operating non-regularities depend upon the operating environment of the air cylinder or other pneumatic device. Thus, the air cylinder characteristics may depend upon the type of damper being controlled, the air flow through the duct, and similar parameters.
Control of such pneumatic devices is difficult, because the hysteretic, frictional, mechanical or other delays result in long settling times as the air cylinder relaxes to a steady state. During this settling time, the pressure transiently varies in the air cylinder. The air pressure regulator attempts to respond to such transient pressure variations by repeatedly switching between pressurizing and exhausting the air cylinder. This can further increase the settling time, and additionally creates noises that travel through the ducts of the HVAC system and can be disturbing to people in the house, office building, or other structure.
The present invention contemplates an improved apparatus and method that overcomes the aforementioned limitations and others.